U.S. patent number 6,374,663 [Application Number 09/404,000] was granted by the patent office on 2002-04-23 for method and device for leakage testing in a tank system.
This patent grant is currently assigned to Volvo Personvagnar AB. Invention is credited to Peter .ANG.lleving, Jan Muller.
United States Patent |
6,374,663 |
Muller , et al. |
April 23, 2002 |
**Please see images for:
( Certificate of Correction ) ** |
Method and device for leakage testing in a tank system
Abstract
Methods for testing leakage in a tank system are disclosed
including sealing the tank system, creating a pressure variation in
the sealed tank system, measuring the pressure values in the sealed
tank system at predetermined time intervals for a measuring period,
and comparing the shape of a curve formed by the measured pressure
values to a predetermined curve for the system, whereby if that
comparison exceeds a predetermined limit value, the leakage test is
disregarded. Apparatus for carrying out such testing is also
disclosed.
Inventors: |
Muller; Jan (Save,
SE), .ANG.lleving; Peter (Alings.ang.s,
SE) |
Assignee: |
Volvo Personvagnar AB
(SE)
|
Family
ID: |
20406821 |
Appl.
No.: |
09/404,000 |
Filed: |
January 10, 2000 |
PCT
Filed: |
April 30, 1998 |
PCT No.: |
PCT/SE98/00799 |
371
Date: |
January 10, 2000 |
102(e)
Date: |
January 10, 2000 |
PCT
Pub. No.: |
WO98/49439 |
PCT
Pub. Date: |
November 05, 1998 |
Foreign Application Priority Data
|
|
|
|
|
Apr 30, 1997 [SE] |
|
|
9701667 |
|
Current U.S.
Class: |
73/49.2; 702/50;
702/51; 73/49.7 |
Current CPC
Class: |
F02M
25/0809 (20130101); F02M 25/0818 (20130101); G01M
3/025 (20130101) |
Current International
Class: |
F02M
25/08 (20060101); G01M 3/02 (20060101); G01M
003/02 (); G01M 003/26 (); G01M 015/00 () |
Field of
Search: |
;73/49.2,49.7 ;702/50,51
;701/29 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Williams; Hezron
Assistant Examiner: Cygan; Michael
Attorney, Agent or Firm: Lerner, David, Littenberg, Krumholz
& Mentlik, LLP
Claims
What is claimed is:
1. A method for on-board evaluation of leakage testing conditions
in a tank system in a motor vehicle, comprising sealing said tank
system, creating a pressure variation in said sealed tank system,
measuring the pressure values in said sealed tank system at
predetermined time intervals for a predetermined measuring period,
and comparing the shape of a first curve formed by said measured
pressure values to a predetermined second curve shape, said second
curve shape being characteristic for a sealed tank system having
fuel sloshing, whereby if said comparison exceeds a predetermined
limit value said leakage test is disregarded.
2. The method of claim 1 wherein said creating of said pressure
variation in said sealed tank system comprises creating an
underpressure in said sealed tank system.
3. The method of claim 1 wherein said creating of said pressure
variation in said sealed tank system comprises creating an
overpressure in said sealed tank system.
4. The method of claim 1 wherein said predetermined second curve
comprises a second degree polynomial.
5. The method of claim 1 wherein said predetermined time intervals
are constant.
6. The method of claim 1 wherein said predetermined limit value is
based upon a condition comprising fuel sloshing.
7. The method of claim 1 wherein the number of said measured
pressure values comprises an odd number.
8. A method for on-board evaluation of leakage testing conditions
in a tank system in a motor vehicle, comprising sealing said tank
system, creating a pressure variation in said sealed tank system,
measuring the pressure values in said sealed tank system at
predetermined time intervals for a predetermined measuring period,
and comparing the shape of a first curve formed by said measured
pressure values to a predetermined second curve shape, said second
curve shape being characteristic for a sealed tank system having
fuel sloshing, whereby if said comparison exceeds a predetermined
limit value said leakage test is disregarded, wherein said
comparing of said shape of said first curve to said predetermined
second curve comprises fitting a function with said predetermined
second curve to said shape of said first curve using the method of
least squares, calculating, squaring and summing the differences
between said function of said predetermined second curve and said
measured pressure values of said first curve, dividing said sum by
the number of said measured pressure values to provide a
predetermined ratio, calculating a curving 2a.sub.2 value for said
predetermined second curve, and comparing said predetermined second
curve to said first curve using said predetermined ratio and said
curving 2a.sub.2 value.
Description
FIELD OF THE INVENTION
The present invention relates to a method for leakage testing in a
tank system and a device for carrying out such a method.
BACKGROUND OF THE INVENTION
The requirements for emission control for motor vehicles constantly
increase. In connection with such requirements, there are also
requirements for detecting that there are no emissions due to leaks
in the tank system of the vehicle. If a leak is detected, this is
usually indicated to the driver by a control system in the vehicle
switching on a light on the instrument panel of the vehicle, a
so-called MIL (Malfunction Indication Lamp). An example of a
requirement regarding detection of leaks in the tank system of a
vehicle is the CARB OBDII Leakage Detection Requirement (California
Air Resources Board, On Board Detection) which requires the
detection of leaks in a tank system which have a flow which
corresponds to the flow through a circular hole, the diameter of
which exceeds a certain given limit, which is currently 1 mm.
One method of detecting leaks in the tank system of a vehicle is to
seal the tank system during a measuring period, and to create an
overpressure or an underpressure in the tank system. If the
pressure in the sealed tank system varies more than a certain
permitted value during the measuring period, this is taken as an
indication of a leak in the tank system. An example of this method
is, for example, that shown in U.S. Pat. No. 5,261,379, which uses
an underpressure.
A drawback of the method of detecting leaks using pressure
variations in a sealed system is that pressure variations can have
other causes than leaks. Transient occurrences such as, for
example, fuel sloshing can cause pressure increases since sloshing
leads to an increased evaporation, and thus to an increased
pressure.
This means that during a leakage measurement there can be other
circumstances, among them fuel sloshing, due to which the results
of the leakage test should not be accepted, since the results of
the test are not reliable.
A method or system for leakage testing which cannot recognize
circumstances which can cause erroneous measurements can function
well in a controlled environment, such as in a test lab where it is
possible to check that such conditions are not present. However,
under real circumstances, such as under normal driving conditions,
such a system will cause erroneous detections of leaks in the tank
system.
In conclusion, there is a need to be able to tell when there are
circumstances in a tank system, for example fuel sloshing, the
presence of which mean that the result of the leakage test should
not be accepted.
The object of the present invention is thus to obtain a method
which can recognize circumstances, the presence of which means that
the result of a leakage test in a tank system should not be
accepted.
SUMMARY OF THE INVENTION
In accordance with the present invention, these and other objects
have now been realized by the invention of a method for testing
leakage in a tank system comprising sealing the tank system,
creating a pressure variation in the sealed tank system, measuring
the pressure values in the sealed tank system at predetermined time
intervals for a predetermined measuring period, and comparing the
shape of a first curve formed by the measured pressure values to a
predetermined second curve, whereby if the comparison exceeds a
predetermined limit value the leakage test is disregarded. In a
preferred embodiment, the step of creating the pressure variation
in the sealed tank system comprises creating an underpressure in
the sealed tank system. In another embodiment, however, the step of
creating the pressure variation in the sealed tank system comprises
creating an overpressure in the sealed tank system.
In accordance with one embodiment of the method of the present
invention, comparing of the shape of the first curve to the
predetermined second curve comprises fitting a function with the
predetermined second curve to the shape of the first curve using
the method of least squares, calculating, squaring and summing the
differences between the function of the predetermined second curve
and the measured pressure values of the first curve, dividing the
sum by the number of the measured pressure values to provide a
predetermined ratio, calculating a curving 2a.sub.2 value for the
predetermined second curve, and comparing the predetermined second
curve to the first curve using the predetermined ratio and the
curving 2a.sub.2 value. In accordance with another embodiment of
the method of the present invention, the predetermined second curve
comprises a second degree polynomial.
In accordance with another embodiment of the method of the present
invention, the predetermined time intervals are constant. In
accordance with one embodiment of the method of the present
invention, the predetermined limit value is based upon a condition
comprising fuel sloshing.
In accordance with another embodiment of the method of the present
invention, the number of the measured pressure values comprises an
odd number.
In accordance with present invention, an apparatus has also been
devised for testing leakage in a tank system comprising sealing
means for sealing the tank system, pressure variation means for
exposing the sealed tank system to a predetermined pressure
variation, pressure measuring means for measuring the pressure in
the sealed tank system, and memory means adapted to store
predetermined pressure values for the tank system and for comparing
the shape of a first curve formed by the measured pressure values
to a predetermined second curve, whereby if the comparison exceeds
a predetermined limit value the leakage test is disregarded.
In accordance with one embodiment of the apparatus of the present
invention, the pressure variation means comprises means for
exposing the sealed tank system to an underpressure.
In accordance with another embodiment of the apparatus of the
present invention, the pressure variation means comprises means for
exposing the sealed tank system to an overpressure.
According to a preferred embodiment of the present invention, the
tank system is first sealed, and subsequently the pressure in the
tank system is lowered. Following this, a number of values of the
pressure in the tank system are then measured during a measuring
period. The curve which is formed by the measured pressure values
is then compared to the shape of a pressure variation curve which
is known to form during circumstances which allow leakage testing.
If the discrepancy between the measured curve and the curve with
which it is compared exceeds a certain predefined limit, a
circumstance is indicated which means that the result of the
leakage testing in the tank system should not be accepted.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be more fully appreciated with reference
to the following detailed description, which, in turn, refers to
the appended drawings, in which:
FIG. 1 is a schematic representation of a tank system in which the
invention is applied;
FIG. 2 is a graphical representation of a curve of the pressure
development in a sealed tank system in the case of an
underpressure, which tank system has a leak with the diameter of
about 1 mm;
FIG. 3 is a graphical representation of the pressure development in
a sealed tank system at underpressure where the tank system does
not have any leaks;
FIG. 4 is a graphical representation of a curve of the pressure
development during fuel sloshing in a sealed tank system at an
underpressure; and
FIG. 5 is a graphical representation of the least square sum (S/N)
and the curving (2a.sub.2) for a number of leakage tests.
DETAILED DESCRIPTION
FIG. 1 schematically shows a tank system 100 in which the present
invention is applied. The tank system comprises a fuel tank 110
which, through a connection 195, provides fuel to the engine system
of the vehicle. The tank system 100 further comprises a so-called
carbon canister 120. The purpose of the carbon canister 120 is to
absorb fuel fumes from the tank system 100. The carbon canister 120
is connected through a valve 130, a so-called Canister Close Valve,
CCV, to an exhaust pipe 140. Furthermore, the carbon canister 120
is connected, by means of a pipe 180, to the engine 190 of the
vehicle, which enables fuel fumes to be sucked into the engine 190
of the vehicle. The connection between the carbon canister 120 and
the engine 190 of the vehicle, the pipe 180, is provided with a
valve 170, a so-called Purge Valve, PV, which is opened when fuel
fumes are to be led from the carbon canister 120 to the engine
190.
When a leakage test according to the present invention is to be
carried out, the system 100 is, in a preferred embodiment, sealed
by closing the connection 195. Following this, in the preferred
embodiment an underpressure is created in the tank system 100. The
underpressure in the tank system 100 is created by leading an
underpressure from the engine 190 into the tank system 100 through
PV 170 and the pipe 180, following which CCV 130 and PV 170 are
closed. The underpressure can also be created in other ways, for
example by a separate evacuation pump. A pressure sensor 150 which
is preferably arranged at the fuel tank 110 and connected to an
engine control unit 160, at predetermined and preferably constant
intervals of time .DELTA.T during a measuring period T provides
values (P.sub.1 -P.sub.N) of the pressure in the tank system 100.
The measured pressure values (P.sub.1 -P.sub.N) are stored in a
memory in the engine control unit 160.
Empirically, the curve-shape which is formed by the pressure
variation as a function of time in a sealed tank system which is in
a state where the result of the leakage test should be accepted is
known. Examples of such curves are shown in FIGS. 2 and 3. The
curves initially exhibit a drop in pressure, created in the manner
described above. When the desired level of the underpressure has
been reached, a measuring period is initiated, as indicated in the
figures. Following termination of the measuring period, the sealed
tank system is again opened, which causes the final pressure
increase shown in the figures.
FIG. 2 shows the curve of the pressure variation as a function of
time in a sealed tank system 100 with a leak of a diameter of about
1 mm, and FIG. 3 shows the corresponding curve of the pressure
variation in a sealed tank system 100 which does not have any
leaks. As can be seen, common to these curves is that they are
concave and relatively smooth.
FIG. 4 shows an example of a curve of the pressure development as a
function of time during fuel sloshing in a sealed tank system 100
without leaks, at underpressure. The curve of FIG. 4 deviates
significantly from the curves which are obtained in the absence of
fuel sloshing, a difference which, as can be seen, is present
regardless of whether there is a leak in the tank system 100 or
not.
As mentioned above, it is known which curve-shape is formed by the
pressure variation as a function of time in a sealed tank system
which is in a state where the result of the leakage test should be
accepted. Due to this knowledge, if the measured pressure values
(P.sub.1 -P.sub.N) are used to form a curve K, it is then possible
to determine, using the curve K, whether the result of the leakage
test should be accepted or not.
To be more precise, this is done by letting the engine control unit
160 fit a predefined curve-shape to the curve K. The final form of
the predefined curve-shape is defined by the fitting. In the
preferred embodiment, the predefined curve-shape is a polynomial of
the second order. Following the fitting, a sum S of the squares of
the differences between the curve K and the polynomial in the
points P.sub.1 -P.sub.N is calculated. A measurement of the curving
2a.sub.2 is obtained from the polynomial. These calculations can be
carried out in the following manner:
Let y.sub.1, y.sub.2, . . . Y.sub.N be a number of measured values
and let X.sub.1, X.sub.2, . . . X.sub.N be the periods in time at
which they were measured.
Additionally let y be an arbitrary second degree polynomial,
y=f(x)=a.sub.0 +a.sub.1 x+a.sub.2 x.sup.2
A curve fitting using the method of smallest squares of y=f(x) to
the curve defined by (X.sub.n, Y.sub.n) where n=1,2, . . . N, can
be obtained from the linear system (1). ##EQU1##
Make the following substitutions ##EQU2##
(1) can then be rewritten as
If x.sub.1, x.sub.2, . . . x.sub.N are symmetrically chosen around
zero, in other words
this means that b.sub.1 =b.sub.3 =0 and (3) can be rewritten as
which can be solved in a simple manner ##EQU3##
A sum of smallest squares S can be calculated as
S=(f(x.sub.1)-y.sub.1).sup.2 +(f(x.sub.2)-y.sub.2).sup.2 +. . .
+(f(x.sub.N)-y.sub.N).sup.2 (7)
The value S is a measurement of how well the fitted curve y=f(x)
follows the curve which is defined by the values in the measurement
series (X.sub.n, Y.sub.n), n=1,2 . . . , N. If N is varied between
the different measuring series, S/N can be used instead. This
enables different measuring series to be compared to each
other.
The second derivative of f(x) is 2a.sub.2.
The curving of f(x) is *f"(x)*=*2a.sub.2*
If f"(x)=a.sub.2 >0 the curve is convex.
If f"(x)=a.sub.2 <0 the curve is concave.
The results of this method applied to real leakage tests with
systems with and without leaks, without fuel sloshing and a system
without leaks with fuel sloshing, are shown (in a logarithmic
scale) in FIG. 5. As can be seen from FIG. 5, there is a clear
difference between systems with and without fuel sloshing. By
determining a suitable threshold level, it is thus possible to
detect the presence of fuel sloshing, and thus also to determine
when the result of the leakage test should not be accepted.
An example of a threshold level is shown by the line T.sub.DET of
FIG. 5.
The present invention is not limited to the described embodiments,
but can be varied within the scope of the appended claims. For
example, the pressure which is created in the sealed tank system
100 can be an overpressure instead of an underpressure.
The comparison between the curve K and another curve can of course
be carried out in a number of ways apart from that shown above. In
the example described, the comparison is made when all the
measurements (P.sub.1 -P.sub.N) have been made. In an alternative
embodiment, the comparison can be made during the measuring
period.
Furthermore, there can be other curve-shapes besides second degree
polynomials with which it is suitable to compare. The interval of
time .DELTA.T between the pressure measurements does not need to be
constant, and the circumstance which does not allow leakage testing
does not of course need to be fuel sloshing, but can be an
arbitrary transient occurrence.
The components used in the device and the method, the pressure
sensor 150 and the engine control unit 160 can be of a large number
of types. Since the choice of these separate components is not of
essential importance to the present invention, they have not been
described above. Although the invention herein has been described
with reference to particular embodiments, it is to be understood
that these embodiments are merely illustrative of the principles
and applications of the present invention. It is therefore to be
understood that numerous modifications may be made to the
illustrative embodiments and that other arrangements may be devised
without departing from the spirit and scope of the present
invention as defined by the appended claims.
* * * * *